If you want to run system-wide Speech Dispatcher (do you have a special
reason for it?), it is easiest to use inet_socket communication method and
in the sessions where you want to use it, set
SPEECHD_ADDRESS=inet_socket:localhost:6560
I think you can do so conveniently in /etc/profile

Thank you for the work-around, but the fact that it doesn't work by default is
still a bug that needs to be fixed.

It is not a workaround, this is how it is done. It is not recommended
to run Speech Dispatcher system-wide. This is why I've asked if you
have a special reason for it.
Normally, user would just start the client (Orca, speechd-el,
spd-say) and the client would autostart Speech Dispatcher
inside the session. This is supposed to work without any
configuration.
Please let me know. I'd of course like to understand what
is your motivation, perhaps other users have it too and we
should try to simplify it for them.
Best regards,
Hynek Hanke